Semi-automatic control systems capable of on-line control of a steam turbine and able to start, load, and unload the turbine in response to a few discrete commands supplied by an operator (e.g., target speed, acceleration, target load, and loading rate) have been known and used for several years. These control systems, implemented largely with analog electronic and electrohydraulic components, have provided very precise control while building a good record of durability and reliability. Nevertheless, there has been a continuing need for a fairly high degree of human interaction with the controller, particularly during periods of non-steady state operation. To provide direction prudently, operators have had to take guidance from turbine stress monitoring instruments and various other instrument systems and monitoring devices. Recently, the scarcity and high cost of energy has fostered the development of larger, more refined, and more efficient turbine-generators for which the electrical utilities have sought means to ensure the ability to start, stop, change loads, etc., in response to changing load demands in the most flexible and economical manner. This has led to the development of highly refined supervisory instrumentation and monitoring systems, but it has also made the duty of the operator more demanding by requiring that he absorb and process an increasing amount of information as he further directs control of the turbine-generator.
To aid operators in these supervisory tasks, large digital computers have been programmed and utilized to supervise and start, load, and unload the turbines by exercising supervision of the above mentioned on-line, semi-automatic control systems. These applications have been fairly successful, although to justify the use of large main-frame computers, turbine supervision and control has been only one of many tasks assigned to the computer. Other tasks commonly assigned include control and supervision of the boiler and power plant auxiliary equipment, performance calculations, sequence monitoring, and data logging. Due to the complexity and diversity of these and other assigned tasks, reliability of control with large computers has not always been as high as is desirable for electrical utility use. Also, because of the cost, not all turbine-generator users have been able to justify a computerized, fully automatic control system.
Accordingly, it is an object of the present invention to provide a dedicated, computerized control system capable of optimally and automatically starting, loading, and unloading a turbine-generator within its thermal and mechanical constraints and to provide this capability without discarding, but rather by building upon, the well-tested, highly reliable analog electrohydraulic control systems.
Another object of the present invention is to provide a lower cost alternative to the large main frame computer for steam turbine-generator control by providing a microcomputer-based, distributed control system dedicated to supervisory control and which is economically justified without the necessity of serving other, auxiliary functions.
A further object of the invention is to provide improved supervisory and protective capabilities in an integrated, dedicated computer control system for a large steam turbine-generator wherein the control system has various operating modes including a monitor mode, a supervisory control mode, and a subloop control mode whereby a large, plant computer, requiring minimal programming, can direct turbine-generator operation and receive reports regarding its progress.
To those skilled in the art, still further objects and improvements offered by the invention will be apparent from the following description of the principles and operation of the invention and of its preferred embodiment.